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Chemistry > AS Organic > Flashcards

AS Organic Flashcards

1
Q

3 characteristics of a homogolous series

A

Same functional group
Same general formula
Consecutive members of a homogolous series differ by CH2 unit

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2
Q

What’s a sigma bond

A

Single covalent bond formed when 2 atomic orbitals on adjacent atoms overlap in a linear manner

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3
Q

What’s a pi bond

A

Covalent bond formed when 2 atomic p orbitals on adjacent atoms overlap in a sideway manner
(The horizontal one above a C=C bond)
They have high electron density - thus easily attacked by electrophiles

Every time you add a bond it’s pi bond

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4
Q

Define stereoisomerism

A

They have the same structural formula but different arrangement on space

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5
Q

When would E-Z isomers arise

A

When there’s restricted rotation in a C=C

When there are 2 different groups/atoms attached to both ends of the bond

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6
Q

What is optical isomerism

A

Occurs in carbon compounds in 4 different groups of atoms attached to a carbon aka asymmetric carbon/ CHIRAL CARBON

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7
Q

What does NOT superimposable mean

A

They are mirror images of each other

Molecules cannot be placed on top of one another and give the same spacial arrangement

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8
Q

What are enantiomers

A

Mirror images of each other

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9
Q

What is a racemic mixture

A

A mixture that contains an equimolar mix of the 2 isomers/enantiomers

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10
Q

How does optical isomers perform in plane polarised light

A

They rotate by the same amount in opposite directions

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11
Q

How does a racemic mixture perform in Plane polarised light

A

It doesn’t rotate

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12
Q

What does chirality mean

A

Mirror image / non superimposable

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13
Q

What is a petroleum fraction

A

Mixture of hydrocarbons with a similar chain length and boiling point range

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14
Q

How does petroleum fraction work

A

The fractions condense at different heights
The temperature of column decreases upwards
Separation depends on boiling points
Boiling point depends on size of molecules
The larger the molecule the larger VDW forces
Similar molecules condense together in which small molecules condense at the top at Lower temp

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15
Q

What is cracking

A

Conversion of large hydrocarbon to smaller hydrocarbon molecules by breakage of C-C bonds

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16
Q

Economic reasons for cracking

A
  • Petroleum fractions with shorter C chains are in more demand than larger fractions
  • Make use of excess larger hydrocarbons and to supply demand for shorter ones
  • Products of cracking are more valuable than the starting material
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17
Q

State the conditions of thermal cracking and what it produces

A

High pressure and high temperature

Produces mostly alkenes eg. Ethene used for making polymers

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18
Q

State the conditions of catalytic cracking

A

Low pressure
High temperature 500
Zeolite catalyst

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19
Q

What does catalytic cracking produce

What do these products do

A

Branched and cyclic alkanes -burns more cleanly

aromatic hydrocarbons

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20
Q

What is catalytic cracking used for, why is it better than thermal cracking

A

Used for making motor fuels

It is cheaper than thermal as lower temp and pressure is used

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21
Q

What can carbon cause

A

Global dimming

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22
Q

Name the 3 steps of FREE RADICAL SUBSTITUTION

A

Initiation
Propagation
Termination

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23
Q

State the condition needed for free radical substitution

A

UV light

Or heat to 300 degrees

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24
Q

What is a free radical

A

A reactive species which has an unpaired electron

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25
Q

What is homolytic fission

A

Where each atom gets one electron from the covalent bond

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26
Q

Recall what happens in the 3 steps of free radical substitution

A

Initiation :
The halogen eg, chlorine, undergo homolytic fission and forms free radicals
Propagation : usually has 2 steps
A chlorine free radical reacts with the Alkane to produce another free radical and a haloalkane
Termination :
2 radicals join together to form the product

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27
Q

Why is SO2 harmful

A

It dissolves in atmospheric water to produce acid rain

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28
Q

How can SO2 be removed

SO2 + _____ -> _____

What can the product then be used for

A

By passing through a scrubber containing basic calcium oxide, which reacts with the acidic SO2 in a neutralisation reaction.

SO2 + CaO -> CaSO3

CaSO3 can be used to make CaSO4 for plasterboard

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29
Q

What facilitated the formation of nitrogen oxide in car engines and

A

The high temp and spark provides sufficient energy to break a strong nitrogen bonds

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30
Q 
Pollutant :                Environmental consequence
NO.                             ?
NO2.                          ?
CO.                             ?
CO2
C
Unburnt hydrocarbon
A

NO is toxic - form acidic gas NO2
NO2 is toxic and acidic, forms acid rain
CO - toxic
CO2 - global warming
C - global dimming and respiratory problems
Unburnt hydrocarbon - contribute towards formation of smog

31
Q

What are in catalytic converters that provides large surface area

Name the catalysts

A

Ceramic honeycomb coated with a thin layer of catalyst metals like
Platinum
Rhodium
Palladium

32
Q

What are alkane fuels

A

Releasing energy when combusted

33
Q

Why are alkanes not reactive

A 
Lacks polarity (CH bond nonpolar)
Strong covalent bonds
34
Q

What’s a nucleophile

A

Electron pair donor

Donates their lone pair of electron to form a dative covalent bond

35
Q

Out of chlorine iodine Florine and bromine, which one undergoes the fastest rate of substitution and why

A

Iodoalkanes are the fastest to substitute and fluoroalkanes are the slowest because C-I bond is the weakest thus the easiest to break

36
Q

What is hydrolysis

A

It is the splitting of a molecule by a reaction with water

37
Q

Out of Cl, I, Br, which one is the fastest to form precipitate with silver nitrate

A

Silver iodide forms the fastest.

It has the weakest bond and it is the most reactive

38
Q

What is the mechanism, condition and reagent for the reaction of turning halogenoalkane to alcohol

A

Nucleophilic substitution
KOH
Heat under reflux in aqueous solution

39
Q

Why is AQUEOUS condition so important in the nucleophilic substitution reaction of turning halogenoalkane to alcohol

A

Because if ethanol is used as solvent, elimination reaction occurs instead

40
Q

Tertiary halogenoalkane undergo nucleophilic substitution (to turn alcohol) a different way, why and how

A

The halogen bond breaks first instead of having the nucleophile attack it. The nucleophile then starts attacking the intermediate.

This is because tertiary carbocations is stabilised by the electron releasing methyl groups around it. Also the bulkiness prevent OH ion from attacking any other way.

41
Q

What is the mechanism, reagent and condition for the reaction from haloalkane to nitrile

A

KCN dissolved in ethanol
Nucleophilic substitution
Heating under reflux

42
Q

What do you add when you need to first increase carbon chain in organic synthesis

A

Add KCN so it turns into nitrile

43
Q

Name the mechanism, reagent and condition for turning halogenoalkane to amine

A

NH3 dissolved in ethanol
Heating under pressure
Nucleophilic substitution

44
Q

What is elimination

A

Removal of small molecule (often water) from the organic molecule

45
Q

What is the role of OH- in an elimination reaction, how come?

A

It acts as a base because it attacks the Hydrogen instead of the carbon.

46
Q

What is the mechanism when you go from halogenoalkane to Alkene?
What is the reagent, condition

A

Elimination reaction
KOH (with OH acting as base)
Condition: heat in ethanol

47
Q

What is a SN2 reaction

A

S stands for substitution, N for nucleophilic, and the 2 is because the initial stage of the reaction involves two species

48
Q

What is a electrophile

A

An electron pair acceptor

49
Q

Name the mechanism that turns alkene into halogenoalkane/dihalogenoalkane

A

Electrophilic addition

50
Q

What is the typical condition of electrophilic addition reaction

A

Room temp

51
Q

Why is a carbonation with 2 methyl group attached on the sides more stable

A

Methyl groups are electron releasing and reduces the charge on the ion which stabilises it

52
Q

Know how H2SO4 structure is drawn

A

H-O-S=O

H-O- =O

53
Q

What are the steps when H2SO4 is used in an elimination reaction to form alcohol from alkene? What is the role of H2SO4? How do you know

2 steps is needed in this, thus room temp is the only condition required

A

Stage1- electrophilic addition where you add H2SO4 onto it
Stage2- hydrolysis by adding water then forming alcohol

Sulphuric acid acts as a catalyst because it is regenerated

54
Q

State the 3 essential conditions of hydration of alkenes to form alcohols
CH2=CH2 + H2O -> CH3CH2OH

A

High temperature 300-600
High pressure 70atm
Conc H3PO4 catalyst

55
Q

Costs and Benefits of hydration of alkene to form alcohol

A

There are no waste products and so has a high atom economy

High pressure means it can’t be done in the laboratory and has to be performed industrially

56
Q

What reagent is used for oxidation reactions

A

Potassium dichromate solution and dilute sulphuric acid

57
Q

What is the name of reaction, reagent and condition for primary alcohol to form aldehyde

A

Partial oxidation
Dilute H2SO4 and K2Cr2O7
Limited amount of dichromate, warm gently and distill out the aldehyde as it forms

58
Q

What is the observation when undergoing oxidation

A

Orange dichromate ion (Cr2o7^2-) reduces to green Cr3+ ion

59
Q

What is the name,reagent and condition when a primary alcohol forms carboxylate acid

A

Full oxidation
Dilute H2SO4 and K2Cr2O7
Heat under reflux and use excess dichromate

60
Q

Name the reaction, reagent and condition when secondary alcohol forms ketone

A

Oxidation
Dilute H2SO4 and K2Cr2O7
Heat under reflux

61
Q

Name the reaction when alcohol -> alkene

Name the reagents and their roles

What’s the condition

A

Acid catalysed elimination

Conc H2SO4/ phosphoric acid (acts as catalysts/dehydrating agent)
They provides H+

Warm (under reflux)

62
Q

What are the 2 methods of forming ethanol

A

Fermentation and industrial formation from ethene

63
Q

Conditions needed for fermentation

A

Yeast
No air
Temp 30-40

64
Q

Why is fermentation done in the absence of air

A

The presence of air can cause extra reactions to occur, it oxidised ethanol to produce ethanoic acid

65
Q

Why is an optimum temp needed for fermentation

A

At lower temp, reaction is too slow

At higher temp, the yeast dies and enzyme denatures

66
Q

What are the pros and cons of fermentation

A 
Pro-
Sugar is renewable resource
-cheap
Cons-
Batch process which means it’s slow
Ethanol is not pure which means it needs purifying by fractional distillation
67
Q

Equation for fermentation

A

Glucose -> ethanol and Co2

C6H12O6

68
Q

If ethanol is formed from ethene, what reaction is this

A

Hydration/addition

69
Q

Essential conditions for forming ethanol from ethene

A

Strong conc h3po4
High pressure 70atm
High temperature 300

70
Q

Pros and cons of producing ethanol from ethene

A 
Pros-
Faster
Purer
Continuous process
Cons-
Expensive
Ethene is non renewable
71
Q

What does the term carbon neutral means

A

No net carbon emissions to the atmosphere

72
Q

How is ethanol produced from fermentation regarded as carbon neutral

Use equations

A

As any co2 given off when biofuel is burnt would have been extracted from air by photosynthesis

6CO2 + 6H2O -> C6H12O6 + O2
C6H12O6 -> 2CH3CH2OH + 2CO2
2CH3CH2OH + O2 -> 4CO2 + 6H2O (when combusted)

73
Q

What’s the reason fermentation may not be carbon neutral

A

If energy for this process comes from burning fossil fuels

Chemistry (12 decks)

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